Asthma affects millions of individuals in the United States, and its morbidity and mortality are increasing. Although evidence supports a role for T-cell mediated airway inflammation in its pathogenesis, the exact role that lymphocytes play is not understood. The Principle Investigator (P.I.) has developed a murine model of asthma in which sensitized and challenged mice develop late phase increases in airways resistance and nearly 100 fold increases in airway hyperreactivity (AHR), which can be adoptively transferred to naive mice by a novel population of lymphocytes that lack surface expression of CD3, but express surface determinants for Thy 1 and CD45RA. The P>I> hypothesizes that; (1) AHR and inflammation characteristic of asthma is initiated by this novel Thy 1 +CD45RA+lymphocyte population; (2) that these cells induce the asthmatic diathesis by producing cytokines or recruiting and/or activating other airway effector cells: and (3) that these cells initiate the asthmatic diathesis, in part by altering the phenotype of lung endothelial cells and/or smooth muscle cells. The specific aims are to; I. Characterize the CD3-. Thy 1+ and CD45 RA+ transferring lymphocyte population(s). The P.I. will: (A) Determine if adoptive transfer is mediated by a single population of CD3- cells expressing both Thy 1 and CD45A:, (B) Isolate, immortalize an characterize a stable clone(s) that mediates this adoptive transfer; (C) Characterize the CD45 isoform surface expression of the cloned transferring lymphocyte population; (D) Determine the mechanism of antigen specificity of this CD-3 transferring lymphocyte population. (E) Characterize the cytokine profile of this lymphocyte population. Particular attention will be devoted to determining if it produces cytokines which differentiate T cells to Th2 phenotype. II. Characterize the leukocyte populations infiltrating the airways of these animals. Immunohistochemistry and in situ hybridization will be used to immunotype and characterize the cytokine profile of the airway cells in these animals. III. Characterize the effector cell populations that mediate the airways effects in this model. The P.I. will analyze the effect of adoptive transfer to immunodeficient mouse strains and to recipient normal mice after in vivo depletion of certain potential effector cell populations. IV. Establish in vitro co-culture models to evaluate the effects of these transferring lymphocytes on the activation of endothelium and smooth muscle. Analysis of this unique model which recapitulates in mice many of the features of human asthma will allow us to precisely define the lymphocyte population(s) responsible for the induction of the asthmatic diathesis and begin to characterize the mechanisms by which they mediate their effects.